The present invention relates generally to lead assemblies for connecting implantable medical devices with selected body tissue to be stimulated by such devices, and more particularly to techniques for providing a secure electrical and mechanical connection between wound elements, such as coil conductors, and mating parts such as electrodes, sensors and the like, employed within such lead assemblies.
Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
Pacemaker leads form the electrical connection between the cardiac pacemaker pulse generator and the heart tissue which is to be stimulated. As is well known, the leads connecting such pacemakers with the heart may be used for pacing or for sensing electrical signals produced by the heart or for both pacing and sensing in which case a single lead serves as a bidirectional pulse transmission link between the pacemaker and the heart. An endocardial type lead, that is, a lead which is inserted into a vein and guided therethrough into a cavity of the heart, includes at its distal end an electrode designed to contact the endocardium, the tissue lining the inside of the heart. The lead further includes a proximal end having a connector pin adapted to be received by a mating socket in the pacemaker. A flexible, coiled or wound conductor surrounded by an insulating tube or sheath couples the connector pin at the proximal end with the electrode at the distal end.
When terminating a wound conductor to an associated electrical element such as a proximal end connector pin, a heart tissue stimulating electrode at the distal end of the lead, a blood oxygen sensor, or other such elements within the lead assembly, there is often no way to statistically ascertain the structural integrity of the termination. These joints must have a high degree of reliability for the implantable product to be acceptable for long term implants such as endocardial type pacing leads. In the past, the only way to verify the joint was to immobilize the mating part and pull on the wound conductor and this technique has been used as the chief test method. The major problem with this approach is that as the winding is pulled unequal tension is applied to the individual strains of the wound conductor. As increased tension is applied to the coil, often one strain breaks sooner than the others yielding erratic test results. The present invention provides an approach that overcomes this test method problem while at the same time providing a very reliable and secure connection between a wound element and a mating component.
Perhaps the primary concern with the laser welding of windings and their electrical connectors is that there must exist a balance between the energy delivered to the respective metal masses. In many known constructions, the laser must simultaneously heat the relatively large mass of the connector and the relatively small mass of the wire ends of the wound conductor.
Another problem associated with connections between wound elements and mating components in present day lead assemblies arises from the use of different alloys for the wound elements and mating components. Since dissimilar alloys have different melt temperatures and other thermal properties, such connections are difficult to weld. Moreover, as lead sizes decrease, problems of manufacturability arise. This is particularly true where crimping is employed to secure the wound component to a mating element. See, for example, U.S. Pat. No. 4,953,564 which discloses a cardiac pacing lead having an extendible fixation helix electrode that is mechanically and electrically connected to a rotatable conductor coil by squeezing the helix and coil together between a crimping sleeve and a crimping core. As the sizes of body implantable leads and their constituent parts become smaller, crimping becomes more difficult because the crimping tools cannot be made sufficiently small. Moreover, the same number of lead windings are not always subjected to the crimping action so that failure stress differs from lead to lead.
Some selective examples of the patented prior art will now be mentioned briefly. U.S. Pat. No. 5,569,883 to Walter et al. discloses laser welding a wire coil to an intermediate ring or the like. U.S. Pat. No. 5,571,146 to Jones et al. discloses laser welding dissimilar materials by means of an aperture within a lead. U.S. Pat. No. 5,385,578 to Bush et al. discloses laser welding a wire coil to a sleeve.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.
The present invention relates to a method of joining a longitudinally extending wound element, or coiled wire strand having a wire end portion, and a mating component of a body implantable lead assembly. In one instance, the mating component may include an integral outwardly projecting ledge member with an aperture for receiving the wire end portion; in another instance, an elongated ribbon member has an aperture for receiving the wire end portion of the wound element; in yet another instance, an elongated ribbon member is turned back onto itself at an end to form parallel spaced apart courses defining a slot therebetween for receiving the wire end portion; in still another instance, a tubular member has a continuous sidewall, an aperture through the sidewall, and a window in the sidewall adversely positioned with respect to the aperture, the wire end portion projecting from the exterior of the tubular member through the aperture and into the interior of the tubular member; and in yet another instance, a tubular member has a continuous sidewall, a first aperture through the sidewall for freely receiving therethrough the wire end portion of the wound element, and a second aperture through the sidewall adversely positioned with respect to the first aperture, also for freely receiving therethrough the wire end portion of the wound element. In each instance, the wire end portion and the mating component are then thermally fused together, preferably by means of a laser.
As already noted, a primary purpose of the invention is to improve a laser weld between a winding and a connector and to achieve this result, the laser beam energy should be distributed equally between the wire and the connector. Formerly, the common weld joint typically comprised a winding screwed onto a cylindrical connector. The very last wind (that is, the wire ends) sets against a shoulder. The shoulder and the last wind (the wire ends) are then welded together in an appropriate manner.
The problem which the present invention solves stems from the fact that the connector requires more laser energy to melt than does the wire. During welding, the laser beam heats both welded components, the connector and the wire (winding) simultaneously. The wire melts and the connector melts, but the wire has a smaller metal mass than the connector. As such, the wire accumulates heat very quickly and the wire can melt easily. The connector has much more metal mass by reason of which heat is drawn out of the weld region. This makes it difficult to melt the metal and to create a weld joint. Therefore, the connector requires more laser energy to melt than does the wire. To have a reliable weld, the beam energy must be specifically balanced between the connector and the wire. Proper beam targeting requires placement of the laser beam not equally on the joint such that more energy is focused on the shoulder side than on the wire. However, it is most difficult for a production line operator to properly target the laser beam on the joint and such failure to properly target the laser beam causes rejects resulting from wire melt down, component overheating, lack of weld, and so forth.
Then, too, a difference in material thermal properties multiplies the energy balance problem. For example, platinum requires much more energy to melt than the commonly used alloy MP35N. Proper beam targeting on dissimilar materials becomes even more critical and difficult to achieve a solid weld than when targeting on similar materials.
Also, this kind of weld configuration has one more problem: wires neck down. When wire ends melt, the melted metal spreads over the connector surface and lack of melting metal occurs. After weld solidification the wire ends attached to the weld have necks down. The neck down makes the weld weaker.
The invention related to the laser weld joint (lead winding to connector) of dissimilar or similar materials.
The connector has a slot and the wire ends go through this slot. The connector/winding joint is designed to with ability to target the laser beam towards to the wire ends coming out of the slot. The wire ends are exposed over the connector to equalize the mass of welded materials of wire and connector. The beam should be directed towards to the wire ends to melt wires ends first to create an extra melted material to protect the wire from neck down and the connector from possible bum through.
The laser beam energy applied to the weld joint melts the wire ends very fast. The melted metal slips down creating a puddle over the surface of the connector. The weld puddle protects the wire in the slot from direct impact of laser beam. The laser beam heats the connector and the puddle fusing components together. The melted metal fills the gaps between wires in the slot and creates some positive weld reinforcement. The wire ends are protected from neck down making the weld stronger.
On FIG. 4 the winding is welded to the transition element, which could be welded to any kind of, connectors rings or other implantable lead component.
All shown weld joints can be welded with equal energy distribution between the wires and connector (or transition element) because the joints with exposed wire ends creates correct heat flow balance between the wires and connector. The length of the exposed wire ends can regulate the heat flow balance. Even if the components are made from different materials with different thermal properties the heat flow can be balanced.
Higher thermal properties of material require less mass of material involved in the welding process. For example, if the connector made from Platinum (high thermal properties) and the winding from MP35N (low thermal properties) to compensate for heat flow misbalance (Platinum requires more energy), the exposed wire ends should be longer than in case when the components made from the same material.
Lower thermal properties of material require more mass of material involved in the welding process. If the connector made from MP35N (low thermal properties) and the winding from Platinum (high thermal properties) to compensate for heat flow misbalance (Platinum requires more energy), the exposed wire ends should be shorter than in case when the components made from the same material.
A primary feature, then, of the present invention is the provision of a significantly improved technique for providing a secure electrical and mechanical connection between wound elements, such as coil conductors, and mating parts such as electrodes, sensors and the like, employed within such lead assemblies.
Another feature of the present invention is the provision of such a technique employing a laser.
Still another feature of the present invention is the provision of such a technique which can achieve a satisfactory connection whether or not the alloys of which the components are fabricated are the same or dissimilar.
Yet another feature of the present invention is the provision of a technique of joining a wound element and a mating component of a body implantable lead assembly, where, in one instance, the mating component includes an integral outwardly projecting ledge member with an aperture for receiving the wire end portion.
Still a further feature of the present invention is the provision of a technique of joining a wound element and a mating component of a body implantable lead assembly, where, in another instance, the mating component includes an elongated ribbon member with an aperture for receiving the wire end portion of the wound element.
Still another feature of the present invention is the provision of such a technique of joining a wound element and a mating component of a body implantable lead assembly, where, in yet another instance, an elongated ribbon member is turned back onto itself at an end to form parallel spaced apart courses defining a slot therebetween for receiving the wire end portion.
Yet a further feature of the present invention is the provision of such a technique of joining a wound element and a mating component of a body implantable lead assembly, where, in still another instance, a tubular member has a continuous sidewall, an aperture through the sidewall, and a window in the sidewall adversely positioned with respect to the aperture, the wire end portion projecting from the exterior of the tubular member through the aperture and into the interior of the tubular member.
Still another feature of the present invention is the provision of such a technique of joining a wound element and a mating component of a body implantable lead assembly, where, in yet another instance, a tubular member has a continuous sidewall, a first aperture through the sidewall for freely receiving therethrough the wire end portion of the wound element, and a second aperture through the sidewall adversely positioned with respect to the first aperture, also for freely receiving therethrough the wire end portion of the wound element.
Still another feature of the present invention is the provision of such a technique of joining a wound element and a mating component of a body implantable lead assembly, where, in each instance, the wire end portion and the mating component are then thermally fused together, preferably by means of a laser.
Yet another of the present invention is the provision of such a technique wherein the resulting connection has an improved weld quality over known techniques, exhibits increased strength, guards against component overheating, and results in an improved appearance.